1. Field of the Invention
The present invention relates to a tie anchor or link for structurally connecting two spaced concrete slabs or layers of a tilt-up wall panel which has a layer of rigid insulation sandwiched therebetween. The invention further relates to a novel panel structure and the method or system for assembling such sandwich panels wherein the tie anchor also acts as a support "chair" and spacer for the reinforcing steel grids during formation of the concrete slabs.
2. Description of the Prior Art
Steel reinforced concrete sandwich panels having an intermediate layer of rigid insulation are generally known in the prior art. It is also known in the prior art to provide structural tying members of various designs which extend through the intermediate insulation layer and are anchored in the spaced concrete slabs. Examples of this type of panel construction are found in the U.S. Patent to Fricker U.S. Pat. No. 4,283,896 and the two U.S. Patents to Haeussler U.S. Pat. Nos. 3,757,482 and 3,996,713. These patents also illustrate the common expedient of passing the concrete slab reinforcing bars or rods through openings in the tie members to structurally connect the spaced concrete slabs. Although not specifically disclosed in these three patents, one method used in forming the concrete slabs is to pour them in a vertical orientation between vertical mold members or forms with the steel reinforcing grid assembly serving to support the tie members during formation of the sandwich panel. The two Haeussler patents illustrate a tubular tie anchor having extremely rigid structural characteristics whereby only one such tie member may usually be used for each composite panel or slab. This is discussed in Haeussler U.S. Pat. No. 3,996,713, the problem being one of accommodating a limited relative mobility of the concrete slabs to accommodate thermal dimensional changes and the like.
The U.S. Patent to Garrett U.S. Pat. No. 4,541,211 illustrates a second type of tie anchor for concrete sandwich panels wherein a metal strap extends completely through the two concrete slabs and the intermediate rigid insulation layer. The Garrett ties additionally connect the vertical form panels so as to maintain them at a predetermined distance during the pouring operation. The strap ties serve to support the reinforcing rods which pass through holes in the body of the ties.
When it is desired to fabricate sandwich panels utilizing horizontal forms, one method has been to support the grids of reinforcing rods for the spaced concrete slabs by such means as holes in the forms as illustrated by U.S. Pat. No. 4,117,639 to Steenson et al. Another common practice is that of initially supporting the reinforcing grid or mesh of metal wires or bars on suitable spacer elements placed in the bottom of the form. U.S. Pat. No. 4,624,089 to Dunker discloses this method of construction and U.S. Pat. No. 3,378,981 to Horne illustrates a typical reinforcing rod chair or support for spacing the reinforcing members for horizontal pouring. In the Dunker patent, the tie anchors extend through the intermediate rigid insulation layer and are embedded in the spaced concrete slabs with the anchors being supported by the reinforcing grid during the pouring of the slabs.
Tie anchors have also been devised in the prior art for mechanically connecting double-wall masonry panels wherein one or both of the panels of the slab comprises bricks or masonry blocks. Examples of this type of construction are found in the Atecheson U.S. Pat. No. 2,261,510 and the Narr U.S. Pat. No. 3,217,457. In these instances, the tie strap must be imbedded in the mortar as the blocks or bricks are laid up in a conventional manner. In the Narr patent, the tie straps are supported by the spaced bricks until the mortar is set about the end of the strap and the concrete slab is cast in a form around the upper ends of the tie straps through which reinforcing rods have been placed. The form for the concrete slab must then be removed before the panel is erected. As may be appreciated this method of constructing brick or block double-wall structures is limited to relatively small size panels.
The construction of relatively large structures such as warehouses, cold storage structures and the like has become extremely competitive with reinforced concrete insulated sandwich walls being one of the common methods of building the structures. These sandwich walls are commonly fabricated in horizontal forms on the ground, either at the building site or at a fabricating yard. The assembled panels are then moved into place and erected at the final building wall position. The problems associated with formation of sandwich panel walls involve not only the positioning of tie anchors with sufficient tensile strength to support the spaced concrete slabs during moving and raising but also considerations of heat transfer from one concrete slab to the other by the tie anchors themselves. This latter consideration becomes of primary importance in the construction of cold storage facilities for instance. Another problem is in devising a method for placing the reinforcing steel grid accurately in the body of the concrete slabs in the successive formation of the two slabs separated by the rigid insulation. In larger building walls which may be as much as 60 feet in height the rebar or reinforcing steel grid for both concrete layers must be tied and held in place in a horizontal plane at the proper distance from the bottom of the form. The grids may weigh several tons depending on the size of the wall being formed. In addition, it is necessary to vibrate the wet concrete during or after pouring for proper settling. This is true of both concrete layers, of course, and having to pick up a collapsed reinforcing grid which has lost its support during the pour or vibrating operation is extremely costly in terms of the amount of time and labor it takes to relocate the grid. Because of the competition in forming the insulated panel walls, time and labor saving have become of paramount concern.